In the field of radio receivers and transmitters, it is common to provide a synthesizer that delivers a selectable frequency for down converting a received radio frequency (RF) signal to an intermediate frequency (IF) or to base band and similarly it is common to use a synthesizer for up converting a base band signal (audio or data) to an IF signal and to an RF signal. A synthesizer typically comprises a VCO and a phase locked loop. The phase locked loop incorporates a divider and by loading an appropriate divisor into the divider, the VCO frequency is divided to a desired injection frequency for the IF stage. In this manner, many different IF frequencies can be selected corresponding to different radio channels. For example, in a narrow band radio telephone, radio channels are typically separated at 25 KHz spacings and it is necessary to tune the receiver and transmitter to a number of different 25 KHz channels across a wide range.
A synthesizer is a particularly expensive element of a radio. Significant effort is directed towards eliminating the need for a synthesizer, but no satisfactory method has yet been devised that eliminates the cost of the synthesizer while still allowing an acceptable level of accuracy in tuning of an injection oscillator signal.
There is a need for an improved method of provision of an oscillator signal that is selectable over a wide range and is setable to a high degree of tolerance over different frequencies across the range. There is a need for a low cost solution that is significantly less expensive than existing solutions.